The Montreal Protocol for the protection of the ozone layer mandated the phase out of the use of chlorofluorocarbons (CFCs). Materials more “friendly” to the ozone layer, such as hydrofluorocarbons (HFCs) e.g. HFC-134a replaced chlorofluorocarbons. The latter compounds have proven to be green house gases, causing global warming and were regulated by the Kyoto Protocol on Climate Change. With the continued concern over global climate change there is an increasing need to develop technologies to replace those with high ozone depletion potential (ODP) and high global warming potential (GWP). Though hydrofluorocarbons (HFCs), being non-ozone depleting compounds, have been identified as alternatives to chlorofluorocarbons (CFCs) and hydrochloro-fluorocarbons (HCFCs) as solvents, cleaning agents and heat transfer fluids, they still tend to have significant GWP. Hydrofluoroolefins (HFO) have been identified as potential alternatives with zero ODP and low GWP.
Hence, numerous documents have provided such HFOs. Methods of preparing hydrofluoroalkenes are known. For example, WO2007/079431 discloses processes for the production of fluorinated olefins, including hydrofluoropropenes. The processes which are broadly described as a single reaction or two or more reactions involve fluorination of compound of the formula C(X)mCCl(Y)nC(X)m to at least one compound of formula CF3CF═CHZ, where each X, Y and Z is independently H, F, Cl, I or Br and each m is independently 1, 2 or 3 and n is 0 or 1. 1234yf is prepared by fluorinating 1233xf into 1,1,1,2-tetrafluoro-2-chloropropane (HFC244bb), followed by dehydrochlorination. 1233xf is prepared by trifluorination of the corresponding chlorinated precursor (CCl2=CClCH2Cl).
EP-A-939071 discloses, among many possibilities, gas-phase fluorination of an halogenated propene (including in the list 1230xa) into a fluorinated propene (including in the list 1234yf).
WO2008/054781 discloses a variety of processes for producing a variety of fluoropropanes and halofluoropropenes by reacting halopropanes or halopropenes with HF optionally in the presence of a catalyst. It discloses a process for making 1234yf by reacting 2,3-dichloro-1,1,1-trifluoropropane (243 db) in the presence of HF, on a catalyst, especially Cr/Co 98/2. Reaction products comprise 1234yf and 2-chloro-3,3,3-trifluoro-1-propene (1233xf), the latter being the main product; other products being 1-chloro-3,3,3-trifluoro-1-propene (1233zd) as well as 245cb and 1234ze which are also formed.
WO2008/002500 discloses a process for making a mixture of 2,3,3,3-tetrafluoro-1-propene (HFO 1234yf) and 1,3,3,3-tetrafluoro-1-propene (HFO 1234ze) by catalytic conversion of 1,1,1,2,3-pentafluoropropane (HFC 245eb) on a dehydrofluorination catalyst.
WO2008/040969 discloses a process comprising dehydrochlorination of 243 db into 1233 (xf as well as zd), followed by a reaction involving formation of 1,1,1,2-tetrafluoro-2-chloropropane (244bb) and later formation of the desired 2,3,3,3-tetrafluoro-1-propene through dehydrochlorination. Example 1 of said document discloses a gas phase reaction at atmospheric pressure of 243 db with HF on a Zn/chromia catalyst, whereby 1234yf and 1233xf are formed, together with a small amount of 245cb. Example 2 of said document discloses a gas phase reaction at atmospheric pressure of 245cb in presence of HF on the same catalyst (contact time 5 sec) whereby 1234yf is formed.
WO2009/015317 discloses the reaction of a chlorinated compound which can be 1,1,2,3-tetrachloro-1-propene (1230xa), 1,1,1,2,3-pentachloropropane (240 db) or 2,3,3,3-tetrachloro-1-propene (1230xf) with HF, in gas phase, on a catalyst and in the presence of at least one stabilizer. This process allows obtaining 2-Chloro-3,3,3-trifluoro-1-propene (1233xf).
US2009/0240090 discloses a process for making 2,3,3,3-tetrafluoro-1-propene (1234yf) starting from a compound of formula (I) CX2═CClCH2X, or formula (II) CX3CCl=CH2 or formula (III) CX3CHClCH2X with X=F, Cl, Br, I. The process comprises three steps, which can be followed by purification. The process includes recycling steps allowing higher conversions and yields.